In the production of semiconductor devices, an integrated circuit substrate is coated with a film of photo patterning resist, exposed to actinic radiation, and developed to define a resist image over the integrated circuit substrate. The resist image can, for example, include both lines and spaces, wherein portions of the photo patterning resist that are removed form the spaces and the portions that remain form the lines. The resist image is transferred to the integrated circuit substrate by modifying the exposed portion of the substrate. Such modification may be performed by removal of a portion of the substrate by etching processes, by implantation of atomic species into the substrate, or by other methods known to those skilled in the art. During such processes, the photo patterned resist lines act as a mask to prevent modification of the portions of the substrate underlying the resist lines. Resolution of the image transferred to the substrate is dependent on the resolution of the resist image.
During exposure of a photo patterning resist on an integrated circuit substrate, some reflection of the actinic radiation off the integrated circuit substrate will typically occur. The reflection causes film interference effects that change the effective exposure intensity within a chip, across the wafer, and from wafer to wafer. Given the variation in effective exposure intensity, an unacceptable amount of line width variation typically occurs. This is especially true in modern manufacturing where laser exposure tools are used as the source of the actinic radiation and reflection is particularly prevalent.
To prevent reflection of actinic radiation into a photo patterning resist, one or more layers of an antireflective coating (A.R.C.) may be provided between a substrate and a photo patterning resist film. A.R.C.s often include a radiation adsorbing dye dispersed in a polymer binder, however, some polymers exist that contain an appropriate chromophore that sufficiently adsorbs the actinic radiation (i.e., the chromophore acts as the dye) such that an additional adsorbing dye is not required. The A.R.C. may be adapted to attenuate a particular wavelength of radiation used to expose the photo patterning resist by a selection of suitable adsorbing dyes or a polymer having suitable chromophores.
The use of an A.R.C. however is not without problems. Once the photo patterning resist film is developed, exposing the underlying A.R.C., the A.R.C. must be removed to expose the underlying integrated circuit substrate for subsequent modification as mentioned above. Commonly, the A.R.C. is removed using a reactive ion etch process, however, other types of dry etching or wet etching as known to those skilled in the art may be used.
Bottom antireflective coatings (B.A.R.C.s) generally come in two classes, the developer soluble class in which the B.A.R.C. is dissolved in the developer at the time of the resist development, or developer-insoluble B.A.R.C.s in which the image is transferred through the B.A.R.C. in a dry etch step. The developer soluble B.A.R.C.s are typically materials that are slightly soluble in the developer and dissolve isotropically as soon as the resist above them dissolves during the development process. The logical consequence of this is that there is significant undercutting of the resist as the B.A.R.C. dissolves away underneath it, and there is a sloped B.A.R.C. edge profile. The undercutting and sloped profile promote lift-off of small resist features and limits the resolution of such B.A.R.C.s. Thus currently available developer soluble B.A.R.C.s do not have the needed high resolution (e.g., in the sub-quarter micron range) and do not meet the needs of processes such as shallow implants, described below. Therefore, all high resolution B.A.R.C.s that are currently used are developer insoluble. Thus, generally inorganic B.A.R.C.s are of the developer insoluble class, as are most of the high resolution organic B.A.R.C.s. The reason for this has been set forth above—i.e., due to the problem of avoiding footing or undercuts with what is essentially an isotropic wet etch process of the B.A.R.C. Even if the B.A.R.C. dissolution rate is exactly matched to that of the resist in the correct exposure state for imagewise printing, an undercut-free and foot free, vertical profile is achieved at best only for an infinitesimally short moment. While this can be accepted for larger features, this behavior leads to a low process latitude for high resolution imaging (see FIG. 1).
For a number of applications, e.g., for shallow implants, it is desirable to avoid damage to the substrate by plasma processing. At the same time, control of reflections from the surface and control of the swing curve may make the use of a B.A.R.C. desirable. These technical requirements together can be met by the use of a developer-soluble B.A.R.C., but not if high resolution, e.g., in the sub-quarter micron region, is desired. Currently, there appear to be no B.A.R.C.s that both avoid dry etching and provide sufficient resolution for the above mentioned applications.
The present invention resolves this impasse by providing a first minimum B.A.R.C. that is developed at the time of resist development. It resolves the issue of poor sidewall control by using a photosensitive B.A.R.C., or, expressed in an alternative way, a highly dyed photoresist on which a second photoresist imaging layer can be applied without or with only minimal intermixing. The photosensitive B.A.R.C. of the invention is exposed during the photoresist exposure step; there is no second exposure step following the photoresist development. The exposure of the B.A.R.C. to light generates a solubility gradient in the B.A.R.C. that makes it possible to achieve an anisotropic component in the B.A.R.C. dissolution, as opposed to the isotropic development of conventional developer-soluble B.A.R.C.s.
U.S. Pat. No. 6,110,653, issued Aug. 29, 2000, to inventors Holmes et al., discloses a method comprising the steps of applying a radiation adsorbing layer on a substrate and forming an acid sensitive, water insoluble A.R.C. therefrom, applying a photo patterning resist (PPR) layer on the A.R.C., exposing part of the PPR layer to actinic radiation, developing the PPR layer to form a resist image, rendering the A.R.C. water soluble, and developing the A.R.C. to uncover selected portions of the substrate.